1. Field of the Invention
This invention relates to electronic music synthesis and in particular is concerned with the creation of musical tones which have anharmonic overtones.
2. Description of the Prior Art
For several acoustic musical instruments tones are produced for which the overtones are not true harmonics (integer multiples) of the fundamental frequency of the tone. The most familiar example of such an instrument is the conventional piano. Musical tones having anharmonic overtones have a characteristic timbre which is distinct and easily distinguishable from the timbre of tones having pure harmonic overtones.
Various systems have been described for electronic tone generators which are capable of creating tones with anharmonic overtones. In U.S. Pat. No. 3,888,153 entitled "Anharmonic Generation In A Computor Organ" a system is disclosed for producing tones having anharmonic overtones. Apparatus is described for creating, in real time, tones in which the fundamental frequency is at the true nominal musical pitch but in which the overtones are displaced from the true harmonic frequencies. The frequency displacement of the overtones is such that if an amount d is used for the second harmonic, then 2d is used for the third harmonic, and (n-1)d is used for the n'th harmonic.
In U.S. Pat. No. 4,112,803 entitled "Ensemble And Anharmonic Generation In A Polyphonic Tone Synthesizer" apparatus is disclosed for producing an ensemble effect in a polyphonic tone synthesizer of the type wherein musical notes are produced polyphonically by computing a master data set, transferring the master data set to buffer memories, and repetitively converting in real time the contents of these memories into musical tones. A multiplicity of master data sets are created repetitively and independent of the tone generation by computing a Fourier algorithm using stored sets of harmonic coefficients. The phase of such master data sets are generated with time varying phase shifts to provide the out-of-tune ensemble effects. The phase shifted master data sets are combined and transferred to buffer memories from which data is converted into musical sounds. Anharmonic overtones are produced by inhibiting the phase shifts of the fundamental frequency components.